Melamine is a common chemical recently found to have been added to animal feed in an attempt to increase the apparent protein content of the product. As a result, a substantial amount of the animal feed that entered the consumer market was contaminated, killing a large number of animals. Current methods of detecting melamine and other contaminants are labor-intensive and time consuming. There exists a need for rapid, non-destructive, specific, low-cost, and routine systems and methods for assessing feed samples for the presence or absence of melamine. Additionally, it would be helpful to be able to detect other contaminants such as cyanuric acid, ammeline, and ammelide, which may also be found in feed materials. These agents may be present in due to their individual addition to the feed or as a result of melamine degradation.
Fast melamine screening requires minimal sample preparation (e.g., no extraction/centrifugation), routine analysis of a number of samples without reagents, minimal procedures and ease of operation. Such systems and methods are increasingly important because of the potential public and animal health concerns. In addition, systems and methods are needed for melamine screening to prevent protein fraud.
Spectroscopic imaging combines digital imaging and molecular spectroscopy techniques, which can include Raman scattering, fluorescence, photoluminescence, ultraviolet, visible and infrared absorption spectroscopies. When applied to the chemical analysis of materials, spectroscopic imaging is commonly referred to as chemical imaging. Instruments for performing spectroscopic (i.e. chemical) imaging typically comprise an illumination source, image gathering optics, focal plane array imaging detectors and imaging spectrometers.
In general, the sample size determines the choice of image gathering optic. For example, a microscope is typically employed for the analysis of sub micron to millimeter spatial dimension samples. For larger objects, in the range of millimeter to meter dimensions, macro lens optics are appropriate. For samples located within relatively inaccessible environments, flexible fiberscope or rigid borescopes can be employed. For very large scale objects, such as planetary objects, telescopes are appropriate image gathering optics.
For detection of images formed by the various optical systems, two-dimensional, imaging focal plane array (“FPA”) detectors are typically employed. The choice of FPA detector is governed by the spectroscopic technique employed to characterize the sample of interest. For example, silicon (“Si”) charge-coupled device (“CCD”) detectors or CMOS detectors are typically employed with visible wavelength fluorescence and Raman spectroscopic imaging systems, while indium gallium arsenide (“InGaAs”) FPA detectors are typically employed with near-infrared spectroscopic imaging systems. For some modalities, intensified charge-coupled devices (“ICCD”) may also be used.
Wide-field spectroscopic imaging of a sample can be implemented by collecting spectra over the entire area encompassing the sample simultaneously using an electronically tunable optical imaging filter such as an acousto-optic tunable filter (“AOTF”) or a liquid crystal tunable filter (“LCTF”). Here, the organic material in such optical filters are actively aligned by applied voltages to produce the desired bandpass and transmission function. The spectra obtained for each pixel of such an image thereby forms a complex data set referred to as a hyperspectral image which contains the intensity values at numerous wavelengths or the wavelength dependence of each pixel element in this image.
Spectroscopic devices operate over a range of wavelengths due to the operation ranges of the detectors or tunable filters possible. This enables analysis in the Ultraviolet (“UV”), visible (“VIS”), near infrared (“NIR”), short-wave infrared (“SWIR”), mid infrared (“MIR”) wavelengths, long wave infrared wavelengths (“LWIR”), and to some overlapping ranges. These correspond to wavelengths of approximately 180-380 nm (“UV”), 380-700 nm (“VIS”), 700-2500 nm (“NIR”), 850-1800 nm (“SWIR”), 650-1100 nm (“MWIR”), 400-1100 (“VIS-NIR”) and 1200-2450 (“LWIR”).